Jose Mourinho and Sir Alex Ferguson were last night warned they cannot bully or intimidate referees this season.

With Chelsea and Manchester United getting the campaign underway with tomorrow's Community Shield at Wembley, referees' chiefs have told Fergie and Mourinho to set the right tone.

And with refs determined to improve the image of football with a disciplinary crackdown, high-profile stars like Wayne Rooney, Cristiano Ronaldo and Didier Drogba were also warned to cut out swearing and diving.

Fergie and Mourinho have been told they will be wasting their time this season trying to bully officials into getting their own way.

Former Premier League ref Neale Barry, now senior head of refereeing at the FA, laid it on the line last night as he said: "There must be fair play on the field and managers must behave the right way in the technical area. We have some very excitable managers but they are ultimately responsible for their conduct.

"No-one wants to see managers acting irresponsibly in the technical area, berating referees, their assistants or the opposition.

"That's not good for the image of the game and everyone needs to accept their responsibilities." And his warning was reiterated by Premier League referees' chief Keith Hackett, who will meet Chelsea's Mourinho and other southern-based Premiership bosses on Tuesday. "Referees must be allowed to deal with incidents and managers mustn't pile in and create more of a problem," said Hackett.